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Stolen Code Is Linked to Program for Chess

Players who use computers to cheat are a growing concern in the chess world. Now the developer of Rybka, the winner of the last four World Computer Chess Championships, has been accused of plagiarizing code to create the program.

Rybka has been stripped of its titles, and the developer, Vasik Rajlich, has been barred from entering programs in competitions.

The ruling on Rybka and Mr. Rajlich was made Tuesday by the International Computer Gaming Association, the group that organizes the championships. It concluded that Mr. Rajlich, who has American and Czech citizenship and lives in Poland, had used source code from programs called Crafty and Fruit.

“We are convinced that the evidence against Vasik Rajlich is both overwhelming in its volume and beyond reasonable question in its nature,” the association’s executive committee said in a statement.

The group said that by using code from Crafty and Fruit, Mr. Rajlich had violated Rule 2 of its guidelines, which requires that programs must either be original or must name other programmers whose work was used.

Mr. Rajlich, who is an international master chess player, did not respond to an e-mail asking about the association’s accusation and decision.

The group’s president, David Levy, who is also an international master, said in an e-mail that Mr. Rajlich had been invited to defend himself but declined to do so.

When questions were first raised about Rybka earlier this year, Mr. Rajlich wrote on a forum on his program’s Web site that “Rybka is and always was completely original code, with the exception of various low-level snippets which are in the public domain.”

Crafty is an open-source program; Fruit, which was once sold commercially, is now free on its Web site and no longer being developed.

Mark A. Lemley, a Stanford law professor who specializes in science and technology issues, wrote in an e-mail that because Fruit and Crafty are freely available may mean that Mr. Rajlich is not guilty of misconduct if he copied some of the code. But, Mr. Lemley added, “I can see why the Computer Gaming Association might want to prohibit it under its rules.”

Plagiarizing code is nothing new. Mr. Levy wrote in an article this year that a program called Quickstep was found to be almost identical to one called Mephisto in 1989. Only last year, the SquarknII program was banned from the computer chess championships after it was found to differ in only three small respects from the code of Robbolito 0.85g3.

Larry Kaufman, a grandmaster who helped Mr. Rajlich in the development of Rybka, but who now works on a rival called Komodo, said in an e-mail that he believed only earlier versions of Rybka were based on Fruit and Crafty.

“In my opinion, there was reasonable basis for the disqualification of Rybka 1 and any tournament victories that occurred within a year or so of its release,” Mr. Kaufman wrote. “By the time Rybka 3 came out, it was for all practical purposes a completely new program,” he said.

Robert M. Hyatt, the developer of Crafty, who is an associate professor of computer science at the University of Alabama at Birmingham and who participated in the computer association’s investigation, said he was certain that Mr. Rajlich had used some of his code.

Dr. Hyatt said he was concerned about how common plagiarizing was becoming. And he noted that Mr. Rajlich himself had been plagiarized. “We already have a clone of Rybka, and now others have copied that copy and are trying to claim unique authorship,” Dr. Hyatt wrote in an e-mail. “This is not going to die away quickly or quietly it seems.”

A version of this article appears in print on July 3, 2011, on page A6 of the New York edition with the headline: Stolen Code Is Linked To Program For Chess. Order Reprints|Today's Paper|Subscribe